Information recording and reproducing systems for recording and reproducing information on and from a disk type information recording medium for each of sectors thereof are known. For in U.S. Pat. No. 4,545,044, there is disclosed an information recording and reproducing system which uses an optical disk.
The optical disk is usually provided with a guide track which is detectable optically in order to form tracks with a higher density, and by irradiating a recording layer formed on the guide track with a laser light beam converged to about 1 .mu.m, a hole is formed or reflectivity is changed to effect the recording of the information.
Since the recorded dot and the track pitch are about 1 .mu.m, various defects are caused during manufacturing of the optical disk (formation of a guide track, manufacturing of a replica disk, evaporation of a recording material, formation of a protective film, and the like), or defects may occur depending on an environment in which the disk is used. Due to such defects of the medium, sometimes a defective sector is detected in which a reproduction error occurs in an address or data. Further, in an information recording and reproducing system wherein rewriting is impossible due to the properties of a recording material as is the case in a write-once type optical disk, if the recording operation is interrupted during data recording, for example, due to a drive error, it results in the recording of incomplete data in a sector, and it is regarded as a defective sector in file management.
A defective sector identification method in a prior art information recording and reproducing system is disclosed, for example, in Japanese Patent Application No. 60-49035 (1985). Further, a method for using an alternative sector for a defective sector is disclosed, for example, in Japanese Patent Laid-Open Publication No. 60-75931 (1985). The operation for using an alternative sector for a defective sector in an information recording and reproducing system will be described with reference to FIG. 5. For example, it is supposed that defective sectors X1 and X2 exist among sectors S1 to S9 on a track T from which data is intended to be reproduced, and that it is recorded in a registor Rg beforehand that alternative sectors are a sector S1' and a sector S2' on a track T'. First, when the reproduction of the data is started with the sector S1, the defective sector X1 located next to the sector S2 is skipped and the sector S4 is accessed. Further, the defective sector X2 located next to the sector S5 is skipped, and this sector S7 and the sectors following thereto are accessed. Next, the track T' is sought to successively reproduce data from the alternate sectors S1' and S2', and the reproduced data is sent to an area in a main memory to which otherwise reproduced data from the defective sectors X1 and X2 would be sent originally.
However, in the aforementioned system for using an alternative sector, it is necessary to provide within the system a register and a buffer to administer a correspondence table indicating a correspondence between a defective sector and an alternative sector, and to provide a table recording area in the information recording area every time a new defective sector is detected. Thus, overhead is increased both in hardware and software. Moreover, in the operation of replacing the defective sector with an alternative sector, a seek operation is required to access the alternative sector existing on a specific track, and the data processing speed is decreased.